Sec Form 4 Filing - ADAR1 Capital Management, LLC @ Keros Therapeutics, Inc. - 2025-04-09

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person ADAR1 Capital Management, LLC 2. Issuer Name and Ticker or Trading Symbol Keros Therapeutics, Inc. [ KROS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 3503 WILD CHERRY DRIVE, BUILDING 9 3. Date of Earliest Transaction (MM/DD/YY) 04/09/2025 (Street) AUSTIN, TX78738 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/09/2025 P 18,560 A $ 9.3952 ( 2 ) 3,493,404 I By ADAR1 Partners, LP ( 1 ) ( 8 ) Common Stock 04/09/2025 P 16,365 A $ 9.3952 ( 3 ) 743,558 I By Spearhead Insurance Solutions IDF, LLC ( 1 ) ( 8 ) Common Stock 04/09/2025 P/K 325,000 A $ 9.857 ( 4 ) 3,818,404 I By ADAR1 Partners, LP ( 1 ) ( 8 ) Common Stock 04/09/2025 P/K 500,000 A $ 10.33 4,318,404 I By ADAR1 Partners, LP ( 1 ) ( 8 ) Common Stock 04/09/2025 P/K 74,333 A $ 10.33 4,392,737 I By ADAR1 Partners, LP ( 1 ) ( 8 ) Common Stock 254,669 I By ADAR1 SPV I, LP ( 1 ) ( 8 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Cash-Settled Total Return Swaps ( 5 ) 04/09/2025 J( 5 ) 325,000 ( 5 ) ( 5 ) ( 5 ) Common Stock 325,000 ( 5 ) ( 5 ) 624,333 ( 5 ) I By ADAR1 Partners, LP ( 1 ) ( 8 ) Cash-Settled Total Return Swaps ( 6 ) 04/09/2025 J( 6 ) 500,000 ( 6 ) ( 6 ) ( 6 ) Common Stock 500,000 ( 6 ) ( 6 ) 124,333 ( 6 ) I By ADAR1 Partners, LP ( 1 ) ( 8 ) Cash Settled Total Return Swaps ( 7 ) 04/09/2025 J( 7 ) 74,333 ( 7 ) ( 7 ) ( 7 ) Common Stock 74,333 ( 7 ) ( 7 ) 50,000 ( 7 ) I By ADAR1 Partners, LP ( 1 ) ( 8 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ADAR1 Capital Management, LLC 3503 WILD CHERRY DRIVE BUILDING 9 AUSTIN, TX78738 X ADAR1 Partners, LP 3503 WILD CHERRY DRIVE BUILDING 9 AUSTIN, TX78738 X ADAR1 Capital Management GP, LLC 3503 WILD CHERRY DRIVE BUILDING 9 AUSTIN, TX78738 X Schneeberger Daniel 3503 WILD CHERRY DRIVE BUILDING 9 AUSTIN, TX78738 X Signatures ADAR1 Capital Management, LLC, By /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date ADAR1 Partners, LP, By /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date ADAR1 Capital Management GP, LLC, By /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date /s/ Daniel Schneeberger 04/11/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )As the investment manager of ADAR1 Partners, LP and ADAR1 SPV I, LP and as the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP, ADAR1 SPV I, LP and Spearhead Insurance Solutions IDF, LLC. As the general partner of ADAR1 Partners, LP and ADAR1 SPV I, LP, ADAR1 Capital Management GP, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP and ADAR1 SPV I, LP. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Mr. Schneeberger may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP, Spearhead Insurance Solutions IDF, LLC, and ADAR1 SPV I, LP. ( 2 )The reported price is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.21 to $9.5 6, inclusive. ( 3 )The reported price is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.21 to $9.56, inclusive. ( 4 )The reported price is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.13 to $10.60, inclusive. ( 5 )In connection with the purchase of 325,000 securities reported as being purchased in Table 1, ADAR1 Partners, LP and the counterparty to the cash-settled total equity swaps previously reported agreed to reduce the number of notional shares of Common Stock of the Issuer in the applicable basket by a corresponding number of 325,000 shares. As a result, the aggregate number of notional shares of Common Stock of the Issuer in the applicable basket after giving effect to such transactions is 624,333 shares. ( 6 )In connection with the purchase of 500,000 securities reported as being purchased in Table 1, ADAR1 Partners, LP and the counterparty to the cash-settled total equity swaps previously reported agreed to reduce the number of notional shares of Common Stock of the Issuer in the applicable basket by a corresponding number of 500,000 shares. As a result, the aggregate number of notional shares of Common Stock of the Issuer in the applicable basket after giving effect to such transactions is 124,333 shares. ( 7 )In connection with the purchase of 74,333 securities reported as being purchased in Table 1, ADAR1 Partners, LP and the counterparty to the cash-settled total equity swaps previously reported agreed to reduce the number of notional shares of Common Stock of the Issuer in the applicable basket by a corresponding number of 74,333 shares. As a result, the aggregate number of notional shares of Common Stock of the Issuer in the applicable basket after giving effect to such transactions is 50,000 shares. ( 8 )For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, each Reporting Person disclaims beneficial ownership of any such securities, except to the extent of his/its pecuniary interest therein, if any, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or otherwise.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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